Directions

Heat oven to 350°F. Line bottom of two 9-inch-round cake pans with waxed paper. Grease paper.

Mix flour, baking soda and salt.

Beat butter and vanilla in a large bowl with an electric mixer on medium speed until fluffy, about 3 minutes. Gradually add sugar and continue beating 2 minutes. Add eggs, beating until blended after each.

Reduce mixer speed to low. Beat in flour mixture in 3 additions alternately with the buttermilk until well blended, beginning and ending with flour mixture. Batter will be very thick.

Remove 1 1/2 cups batter to a bowl. Stir in the melted chocolate. Drop large dollops remaining vanilla batter into prepared pans, leaving spaces between spoonfuls. Spoon chocolate batter between vanilla batter. Run a knife through the batter a few times for a marbleized effect. (No need to smooth tops since the batter spreads as it bakes.

Bake 30 to 35 minutes until a wooden pick inserted in centers comes out clean. Cool in pans on a wire rack 10 minutes, then invert on rack, peel off waxed paper and cool completely.

Up to 8 hours before serving: Place 1 cake layer upside down on a serving platter. Spread 1/2 cup frosting over top. Top with remaining cake layer, right side up. Remove 1/2 cup frosting for decoration; spread remaining over top and sides of cake. Pipe rosettes of reserved frosting on cake using a pastry bag fitted with a star tip. Decorate with sprinkles. Write birthday message using white tube frosting. Refrigerate until 20 minutes before cutting and serving.MILK-CHOCOLATE FROSTINGBring 1 cup heavy cream

Tips & Techniques

Prep Tip: The cake layers can be baked a day ahead, wrapped in plastic wrap and stored at room temperature. Or, wrapped airtight, they can be frozen up to 3 weeks. Thaw before frosting.